A sport boot is going to do nothing for a horse who already has arthritis in his hock.
Horses don't need extra warmth around their legs (like they do their body) because its mostly bone and tendons with lots of blood flow. Besides, you NEVER leave sport boots on longer than 2 hours because they create and build up heat that can damage the tendons and ligaments.
I primarily barrel race. So my horses wear sport boots on all 4 legs and bells boots on the front. It is cheap insurance against knicks and scrapes in the event my horse steps on another leg while doing speed events. I only put the boots on when we are competing or when we are practicing at home. (and they are taken off immediately when I am done, and the legs are cooled off properly)
Conditioning/trail riding they do not wear the boots.
You do get a little bit of support from the sport boots, but not near as much as the companies claim. Again, I do it more for having physical protection against knicks and over-reaching.
For what you are describing, I would not use sport boots on your horse.
∞•*˚ Βгįťţαňγ ˚*•∞
It is not enough to know how to ride; one must know how to fall.